This invention relates generally to endocardial implantable cardiac leads for implantable stimulators, and more particularly to cardiac lead delivery systems using an introducer catheter.
Implantable medical electrical stimulation and/or sensing leads are well known in the fields of cardiac stimulation, including cardiac pacing and cardioversion/defibrillation, and in other fields of electrical physiologic stimulation. In the field of cardiac stimulation, endocardial leads are placed through a transvenous route to locate one or more sensing and/or stimulation electrodes along or at the distal end of the lead in a desired location in a chamber of the heart or a blood vessel of the heart. A pacemaker or defibrillator implantable pulse generator (IPG) is typically coupled to the heart through one or more of such endocardial leads. The proximal end of such leads typically is formed with a connector which connects to a terminal of the IPG or monitor. The lead body typically comprises one or more insulated conductive wire surrounded by an insulating outer sleeve. Each conductive wire couples a proximal lead connector element with a distal stimulation and/or sensing electrode. An endocardial cardiac lead having a single stimulation and/or sensing electrode at the distal end and a single conductive wire is referred to as a unipolar lead. An endocardial cardiac lead having two or more stimulation and/or sensing electrodes at the distal end and two or more conductive wires is referred to as a bipolar lead or a multi-polar lead, respectively.
In order to implant an endocardial lead within a heart chamber, a transvenous approach is utilized wherein the lead is inserted into and passed through the subclavian, jugular, or cephalic vein and through the superior vena cava into the right atrium or ventricle. An active or passive fixation mechanism is incorporated into the distal end of the endocardial lead and deployed to maintain the distal end electrode in contact with the endocardium position. More recently, endocardial pacing and cardioversion/defibrillation leads have been developed that are adapted to be advanced into the coronary sinus and coronary veins branching therefrom in order to locate the distal electrode(s) adjacent to the left ventricle or the left atrium. The distal end of such coronary sinus leads is advanced through the superior vena cava, the right atrium, the valve of the coronary sinus, the coronary sinus, and into a coronary vein communicating with the coronary sinus, such as the great vein. Typically, coronary sinus leads do not employ any fixation mechanism and instead rely on the close confinement within these vessels to maintain each electrode at the cardiac implantation site.
Early implantable, endocardial cardiac pacing leads incorporated a lumen for receiving a stiffening stylet inside the lumen of the conductor coil. More recently, it has been proposed to diminish the lead body diameter by eliminating the lumen for receiving the stiffening stylet. Without the stiffening stylet, it is necessary to resort to use of another mechanism to pass the lead through the vessel paths identified above and to position and fix the distal end electrode of the lead at the cardiac implantation site in the heart chamber or cardiac blood vessel. One approach for implantation of small diameter endocardial leads employs an introducer catheter surrounding the lead body. The assembled introducer catheter and cardiac lead are advanced to the cardiac implantation site using a stylet carried within a stylet lumen in the introducer catheter. The introducer catheter is then retracted proximally over the lead body and proximal connector end assembly. A difficulty with use of such an introducer surrounding the cardiac lead is that permanently implantable endocardial leads are formed typically with a proximal connector end assembly having a diameter exceeding that of the lead body and conforming to an industry standard so that the connector end assembly can be fitted into and seal with an IPG connector bore conforming to the same standard. Consequently, the introducer has to be made large enough to fit over the enlarged diameter connector end assembly. Such introducer catheter size is typically about 10.5 French. This size constraint detracts from the ability to advance the introducer and lead assembly through small diameter blood vessels. Or the lead has to be made with a small diameter, non-conforming, connector end assembly or without any connector end assembly and therefore requiring connection to an adapter to be made conforming to the standard. This is inconvenient and can result in a diminished reliability.
Thus, a need remains for an introducer catheter for implanting an endocardial cardiac lead that is of a reduced diameter and yet still allows a lead and connector to easily pass therethrough.
The present invention is directed to an introducer catheter for endocardial cardiac lead delivery. In particular, the present invention provides for the reduction of introducer catheter size by implementing unique structures. Specifically, the present invention accomplishes the desired reduction by use of a bilumen catheter wherein a collapsible stylet lumen is included. The stylet lumen deforms to a collapsed condition when the stylet is removed. This allows more clearance for the lead and connector to pass through when removing the catheter.